Enamel-like coatings or decorative layers are being applied to auto glass panes to an increasing extent, e.g. in the form of frame-like, opaque coatings along the edge of auto panes which are inserted into the auto body in accordance with the method of direct adhesion. These enamel coatings prevent visibility through the glass pane onto the adhesive connection and serve to increase the adhesion of the adhesive and to protect the adhesive from damaging UV rays. Opaque colored enamel coatings are also applied onto glass panes for other purposes as a cohesive layer or in interrupted form in order to achieve decorative effects. The enamel-like coatings customary for this application consist of a molten glass phase in which coloring pigments are embedded.
It is known that conductor circuits or radio antennas can be produced on vehicle panes with the aid of silver pastes which are applied e.g. by means of screen process printing and are stoved during thermal treatment of the glass. Wherever silver is to be applied in enamelled zones, it is generally applied onto the enamel or between two layers of enamel in order to remove it from the view of the observer, who looks through the pane from the outside, that is, from the non-enameled side.
The enamels used for vehicle panes generally consist of a glass frit or of a mixture of meltable frits as well as of coloring pigments which impart the desired coloration and the covering capacity to them.
The glass frits conventionally used as base for the enamels generally exhibit the following composition (% by weight):
______________________________________ PbO 48-60 SiO.sub.2 28-35 B.sub.2 O.sub.3 2-6 Na.sub.2 O 1-5 TiO.sub.2 1-4 ZrO.sub.2 1-3 Al.sub.2 O.sub.3 0-3 CdO 0-3 CaO 0-2 ZnO 0-1 K.sub.2 O 0-1. ______________________________________
The oxides of chromium and copper or the oxides of chromium, iron, nickel and/or manganese are used as pigments for black color tones. For grey color tones, in addition to the black pigments cited, other pigments are also used such as tin oxide or titanium oxide, for blue color tones, oxides of cobalt, aluminum, silicon and zinc, and for yellow, lead sulfides, antimony sulfides or cadmium sulfides.
It is known that silver compounds which are applied onto glass or enamel impart a yellowish to brown coloration to it due to transparency effects which coloration is conditioned by the diffusion of the silver ions into the glass.
If, therefore, silver pastes are applied onto the enamels for glass, then the glass exhibits a coloration extending from yellow to brown when looked through, which coloration is only insufficiently covered by the enamel layer.
In order to avoid this phenomenon, which adversely affects the appearance of the enamelled glass, the attempt was made to mask the silver layer to the extent possible by treating the enamel and the silver; however, the results were generally unsatisfactory.